Microfabricated elements, such as micro-mirrors, read/write heads of hard disk drives, acceleration sensors, and electro-acoustic high frequency elements, are widely used in a variety of microelectrical-mechanical systems (MEMS) applications. Measurement of the static or dynamic mechanical motion of these microfabricated elements provides information useful for the design, development, and simulation of such devices.
Mechanical motion and displacements of MEMS devices are characterized using techniques such as laser interferometry, laser Doppler velocimetry, stroboscopic interferometry, and an astigmatic detection method. An astigmatic detection system (ADS) measures translational displacement of a target object along one axis and angular displacement of the object around two axes. An ADS includes an optical path mechanism in which a detection laser beam passes through a lens assembly and is focused on the surface of the object. The object reflects the light back through the lens assembly and to a position sensitive photosensor. The shape and position of a light spot formed on the photosensor is used to analyze the translational and angular displacement of the object. To position the detection laser beam at a desired position on the surface of the object, the object is observed through an external microscope that includes an eyepiece or other imaging device, such as a CCD sensor.